1. Field of the Invention
The present invention relates to an endoscope that is used in the maintenance of industrial plants and buildings, and when performing inspections of interiors of equipment inside which flammable gas or dust is present (for example, the interiors of gasoline tanks, industrial plants, and engines), and when performing inspections of boiler interiors and the like. In particular, the present invention relates to a drive device for an explosion-proof apparatus such as an explosion-proof video system that is able to be used in locations where there is a strong possibility of an explosion occurring.
Priority is claimed on Japanese Patent Application No. 2006-19146, filed Jan. 27, 2006, the contents of which are incorporated herein by reference.
2. Description of Related Art
Conventionally, an endoscope is widely used that, by inserting an elongated insertion portion into a body cavity, makes it possible to observe internal organs inside a body cavity and the like, and, if required, to perform a variety of medical treatments using treatment tools that are inserted through the interior of a treatment tool channel. In addition, in industrial fields as well, industrial endoscopes are widely used for making observations and inspections of damage and corrosion inside boilers, turbines, engines, and chemical plants and the like.
Among endoscopes (i.e., video image systems) that are used in the manner described above, electronic endoscopes (referred to below simply as “endoscopes”) exist that have an image pickup element such as a CCD or the like that photoelectrically converts optical images into image signals located in a distal end portion of the insertion portion. In these endoscopes, a structure is employed in which an observation image of an observation position that is illuminated by illumination light supplied from a light source apparatus is formed on an image pickup surface of the image pickup element, and image signals of the observation image that has been photoelectrically converted by this image pickup element are transmitted to an external device in the form of a signal processing section of a camera control unit (referred to below as a CCU). In the CCU, video image signals are created and endoscope images are displayed on a monitor so that an observation can be made.
This type of endoscope device is formed, for example, by an image pickup section that has a solid-state image pickup element provided at a distal end portion thereof that picks up an image of an observation position and also has a light source that illuminates the observation position, and by a control unit that has a power supply and a signal processing section. The control unit and the image pickup section are connected by a cable that is made up of a plurality of electric wires. The supplying of power from the control unit to the image pickup section as well as the sending and receiving of control signals for controlling the image pickup section and video image signals from the image pickup section and the like are conducted via this cable.
Among endoscopes that are used in the field of industry, there are those that are used in hazardous locations such as the pipes of chemical plants and gas tanks and the like, and in explosive atmospheres and the like (referred to below simply as “hazardous locations”). Instruments that are used in these hazardous locations have to at least satisfy safety standard provisions (described below) for intrinsic safety in order to prevent these instruments from becoming a source of ignition and the like.
Because the image pickup section is inserted into a hazardous location of this type and picks up a video image of the interior thereof, a structure is required to satisfy safety standards relating to the supplying of power by the control unit to the image pickup section. Namely, an endoscope device exists that is an explosion-proof video image device in which a barrier limiting circuit that satisfies the aforementioned safety standard provisions is interposed between the power supply of the control unit, and both the image pickup element and light source of the image pickup section (see, for example, Japanese Patent Application, First Publication No. 2001-75020).
[Explanation of Intrinsic Safety]
Intrinsic safety is regulated by the International Electrotechnical Commission (IEC), ATEX (Europe), FM (America), CSA (Canada), TIIS (Japan), and the like, and explosion-proof apparatuses are certified by a certifying body. The description of the present specification is based on the IEC Electrical Apparatus for Explosive Gas Atmospheres standard IEC 60079 and the IEC Electrical Apparatus for Use in the Presence of Combustible Dust standard IEC 61241. However, portions that substantially correspond to the standards of other countries can also be applied to the standards of these other countries and it is of course unnecessary to exclude these other standards.
Consideration will now be given to the mechanism of explosions in hazardous areas. Explosions are generally induced to occur in an environment in which flammable gas or dust mixed together with oxygen are present, as a result of the temperature of an ignition source rising and exceeding the ignition temperature of the mixed gas or dust. For example, inside a gasoline tank, plant and engine, fuel changes into gas or dust and becomes flammable. Ambient oxygen is also present so that a flammable mixture is generated. In this environment, if an ignition source is present such as described above, there is a danger that the temperature of the ignition source will cause an explosion. In other words, the three elements of an explosion are flammable gas or dust, oxygen, and an ignition source, and if even one of these three is not present, then an explosion cannot occur. Of these, flammable gas or dust and oxygen are present in the environment and intrinsic safety is secured basically by blocking any energy applying elements from an ignition source.
In the IEC, locations where an explosion-proof apparatus may be used are defined according to their danger level as Zone 0, Zone 1, or Zone 2. Namely, Zone 0 is where the danger level is the highest, Zone 1 is where the danger level is next highest, and Zone 2 is where the danger level is the next highest. Dangerous areas are referred to as hazardous areas, while areas that are not dangerous are referred to as Non-hazardous areas.
The apparatus structures are defined as “ia” apparatuses, “ib” apparatuses, and “Type-n” apparatuses. “ia” apparatuses have the highest reliability against explosions, while “ib” apparatuses have the next highest reliability. Here, “ia” apparatuses are able to be used in Zone 0 and Zone 1, while “ib” apparatuses are only able to be used in Zone 1. Apparatuses that are able to be used in Zone 0 or Zone 1 are known as intrinsically safe apparatuses. “Type-n” apparatuses are able to be used in Zone 2.